The minimal number of taste compounds (singly or mixed) that are necessary to match the taste of any other solution is not known. l define a group of compounds that match each other in taste as an "equivalence class". I propose to identify equivalence classes for the majority of this work using a technique called matching, which has seldom been used in taste psychophysics. This method provides a powerful tool to further our understanding of the organization of the taste system. Specifically I will ask whether the taste of one chemical solution may be rendered indistinguishable from the taste elicited by a different chemical solution by varying the strength and composition of one while holding the other constant. This psychophysical approach successfully described the psychophysical laws of color matching and determined the number of color vision coding pathways to be three (trichromacy). The parallel hypothesis for taste (N-geusia) will establish a framework for identifying and describing the psychophysical laws of taste matching and will also help identify the number of distinct coding pathways that encode signals for taste qualities. If the tastes of all sapid substances comprise one or more of the four qualities, then it should be possible to match compounds with complex tastes, like that of saccharin which is described as sweet and bitter, with mixtures of compounds that are more purely sweet and bitter. The ultimate ~goal of this project is to determine the extent to which different stimuli elicit unique qualities of taste, and in so doing, improve the understanding of the psychophysics of human taste sensation.